This invention relates in general to magnetic tape cassette transport apparatus. More particularly, this invention relates to a magnetic tape cassette transport/accessor assembly, which is driven in at least horizontal and vertical directions by means of a sprocket driven, belt drive system. The belt drive is tensioned by a spring dampener assembly which dampens rough and jerky movements of the assembly and effects smooth and gentle acceleration and deceleration thereof.
In applications in which a large amount of information is stored on electronic media (such as the storage of digital information on a plurality of magnetic tape cassettes), it is often desirable that each unit of storage (e.g., magnetic tape cassette), be accessed in a minimum amount of time. For example, it is desirable to minimize the time required to change over from one cassette to another cassette used in a magnetic tape record/reproduce device. Where the cassette storage system includes a large number of cassette storage compartments, it is also desirable that the cassette be transported between a storage compartment and a record/reproduce device, in a manner which minimizes damage to the cassette through rough or jerky movements in the cassette transport device. Thus, a smooth, gentle acceleration and deceleration of the cassette transport assembly is desired.
Various arrangements have been proposed to actuate a transport assembly to transport an object between spaced locations in a storage system. The simplest type of arrangement uses manual power for actuation of the transport system. (See: U.S. Pat. No. 4,113,119, issued Sept. 12, 1978, entitled APPARATUS FOR LOADING ARTICLES ONTO VERTICALLY SPACED HORIZONTALLY DISPOSED SHELVES.) Although such an arrangement is relatively inexpensive, it is disadvantageous because it is not readily adaptable for use as an automatic storage system. Moreover, manually initiated movements tend to be abrupt and jerky, causing possible damage to objects being transported. It has been proposed to use motors in order to actuate the transport assembly. Typically, at least one or more of the actuating motors are mounted on the transport assembly itself. (See, for example, U.S. Pat. No. 3,557,977, issued Jan. 26, 1971, entitled LOAD DETECTING DEVICE FOR WAREHOUSING SYSTEM, and U.S. Pat. No. 4,614,474, issued Sept. 30, 1986, entitled DEVICE FOR EXCHANGING DISKS.) However, drive motors and drive motor supports, add considerable weight to the transport assembly, thus increasing the stresses on the transport assembly drive and on the transport assembly load-bearing components. Moreover, reliability is reduced and maintenance is made more difficult and gentle, smooth movement of the assembly is more difficult.
It has been proposed to use a belt or cable system to eliminate mounting one or more motors on moving components of the transport assembly. Thus, for example, in U.S. Pat. No. 4,507,044, issued Mar. 26, 1985, entitled ROBOT AND CONTROL SYSTEM, and U.S. Pat. No. 4,566,346, issued Jan. 28, 1986, entitled AUTOMATED TOOL MANIPULATING STRUCTURE WITH X-Y MOVEMENT INCLUDING A BELT AND PULLEY DRIVE ARRANGEMENT, there are disclosed arrangements in which x and y direction drive motors are not mounted on the member which is moved in the x and y directions. Although these arrangements may be suitable for the purposes for which they were intended, they do not solve the problem of rough and jerky movement of the driven assembly. Although spring tensioning devices have been proposed for use in belt and chain driven assemblies (See, e.g., U.S. Pat. No. 4,476,508, issued Oct. 9, 1984, entitled APPARATUS FOR RECORDING FLEXIBLE MAGNETIC DISKS; U.S. Pat. No. 4,198,871, issued Apr. 22, 1980, entitled TRANSDUCER POSITIONING APPARATUS; and U.S. Pat. No. 4,637,773, issued Jan. 20, 1981, entitled INDUSTRIAL ROBOT OF THE ARTICULATED ARM TYPE), such devices are not suitable for use in a belt drive system for a magnetic tape cassette transport system. In the latter system, it is desirable to transport a magnetic tape cassette in a manner which prevents damage to the cassette and the tape contained therein.